Got my kit late last week and put it together Saturday evening. I'd say it was 4-5 hours of assembly, but 1-2 was dealing with one issue I'll outline below. I did have an advantage in that I'd previously assembled one of the old kits where you had to actually install the X rail yourself, align the vertical smooth rods, and everything. This build is MUCH simpler than that. The major sections are installing the belt + everything above the carriage on the X rail and installing all the wiring harnesses. I did modify things slightly since I already knew I was going to leave off the fan guards on all the extruder fans. There isn't really hardware in the kit to support doing that, so I had to swap in stuff I already had and an M4 nut as a spacer on the long screw into the extruder motor.

Instruction quibbles:There's, like, 3 different instructions on where and how to secure the Heated Build Plate cable/flex tube thing. (Which is an awesome upgrade over plain cable + nylon mesh, BTW.) Two of them suggest attaching it to a zip tie anchor, one of those suggests routing it over all the other cables, and all of those are incompatible with the instruction to attach it to the bottom right inside of the frame with the provided clamp and screw. IMHO, the clamp is all you need, and it should be routed and secured before securing any of the other cable harnesses. It seemed much more natural to route the X harness over the top of the HBP cable, since the HBP cable is now firmly snuggled into that lower right corner.

Also, there should probably be a recommendation to check the fit of the metal electronics enclosure. Mine was slightly off, so the side opposite the frame was distorted upwards slightly, where it would interfere with the Y-axis when the Z was at the bottom. Some judicious elbow grease to bend the frame side of the enclosure inwards a hair persuaded it to stay down.

The one issue:It was a royal pain to get the filament drive to line up with my hot end. It involved modifications that I would not recommend to someone not comfortable with playing with gearbox guts. The issue was the holes in the gearbox absolutely wouldn't let me line up the filament path with the hot end entry. Here's a pic with the filament drive rotated as far clockwise as possible:

Best alignment as recieved

Looking at the front of the gearbox, you can see the hole pattern is distinctly rotated counter-clockwise, despite the faceplate being rotated as far clockwise as possible:

Gearbox face

I think there was a combination of holes being slightly off, and I ended up with the far side of the bell curve. My final solution was to flip the ring gear over, which actually changed things, proving the threaded holes in the ring gear were off a bit. Plus drilling out the holes in the face plate a hair to let me rotate it a little more clockwise. All that means my clockwise limit is now here:

"Fixed" alignment

Which lets me back off a little so nothing's screwed down under strain to keep the alignment. I suspect I just got an unlucky motor for that much modification to be needed. Yes I could've emailed support and gotten a replacement, but I was impatient.

With this problem, the enclosure fit problem, and one dodgy screw I ran into, I think you can see the potential issues with handing these kits out to beginners. When MG fully assembles a printer, they can just set aside any problem parts and grab another out of stock to make sure the assembled printer is perfect. When I'm assembling a kit in my office, I've got exactly as many of the critical components as I would need. So any issues with parts involves either an exchange with support, or working things out yourself.

Quick Start App:This does, in fact, make bed levelling pretty fast and easy for beginners. 3 point levelling was pretty easy if you had a system, but putting the system into software definitely helps. I was somewhat annoyed by the bump up/down arrows. It seems like the 1mm bump was limited to 3 bumps up. And then I had to go another 7-8mm bashing madly on the 0.1mm up button. I can understand putting a purposeful limit there if the levelling routine usually starts closer to the bed on an already levelled machine, but it does make the first levelling a little more like a "clicker" flash game than it probably should be.

Impressions of the M2 Rev E kit vs. my former circa 2014 Rev D kit:Solid spider is solid. I can see why the move to it and 4-point levelling. Once you get that locked in, something has to go pretty wrong to unlevel it. The DIY modifications to turn a 3-point spider into a 4 point one will only get you part way there.The flex tube covering for the HBP wires is a huge step up. My old kit had the wires carrying all the strain and flex, and they had a tendency to float above the bed and rub the x-gantry on large prints. That would push the bed down a hair, and give me a difficult to diagnose extreme first layer spacing problem on larger prints.Also, the beefy metal clamp securing the flex tube to the HBP looks to mean I never have to worry about flexing those wires to the breaking point. Downside is the cable does stick out behind the machine farther than before.Metal Enclosure not as difficult to pack all the wiring into as I'd feared. Actually a bit easier than the old laser-cut enclosure.Oh my gosh, there's an on-off switch on the power supply. I don't have to unplug it or turn off my power strip anymore.

Overall quite pleased with the kit and the build. I do hope for MG's sake that my problem with the filament drive was a rare one though.

That was my first attempt, plus twisting the motor in the metal motor mount. Then I loosened the screws on the back of the gearbox as well, but it still didn't move much. I don't think the screws on the back could help at all, since those holes were drilled and not truly counterbored. The screws wanted to center up on the mild countersink left by the drill. During that process I noticed that the threaded holes in the ring gear must have been off, because one of them was misaligned with the hole in the back plate, and the misalignment followed the ring as I rotated it.

The next step was flipping the ring over (front to back) to see what that did. That got me barely aligned when I torqued everything clockwise, but I wasn't comfortable with having to depend on the screws through the filament drive holding it in place under tension, so finally, I slightly drilled out the holes under the four black screws on the face to get just a little more twist.

In case anyone's questioning my sanity at this point, my hobby is building robots with high schoolers for the FIRST competition. I've developed a little experience with and tolerance for questionable gearboxes and having to fudge them a little to get them working.

On checking the motors when you pack them, I think you could draw up a jig to check the motors pretty easy. Just a box to snug over that back plate of the gearbox with a clearance hole for the shaft and four holes 90 degrees apart at the proper alignment. A little experimenting and you could size those holes to a tolerance that should guarantee someone can easily align the drive, without rejecting every motor that's not dead on perfect.

I don't really have an answer for the motors that don't pass. Maybe they're for dual extruder machines?